They then adjusted my Fed and State withholding to cover SSI.
Please clarify what you mean when you say
"They then adjusted my Fed and State withholding to cover SSI."
You might ask your former employer if they intend to issue a 1099 to you for the value of the vehicle.
Duplicate question answered here:
https://ttlc.intuit.com/community/retirement/discussion/re-should-the-company-i-retired-from-include-the-value-of-a-vehicle-they-gave-me-in-my-w-2/01/2839869#M185126
They reduced my withholding on fed and state on the w-2 to cover SSi withholding.